Mexican sunflower (Tithonia diversifolia (Hemsl.) A. Gray) is a tropical herb or shrub cultivated in many countries of Africa, Asia, and South America for its multipurpose value. As fodder, it is rich in protein, valuable for ruminants and rabbits, but less for poultry and pigs, probably due to the presence of fibre and antinutritional factors.

Morphology

Tithonia diversifolia is a woody herb or succulent shrub, stoloniferous, annual or perennial, that can reach a height of 2 to 3 m (Gualberto et al., 2011). It has a taproot with many fine secondary roots (Mwango et al., 2014). The herbaecous mass can develop from subterranean stolons. The leaves are alternate or opposite, sub-ovate, densely pubescent, 5-17 cm long x 3.5-12 cm broad. Each mature stem may bear several large yellow flowers, up to 12 cm in diameter (CABI, 2014; GISD, 2012; Orwa et al., 2009).

Utilisation

Mexican sunflower is used for a variety of purposes: ornamental, fuel, compost, land demarcation, soil erosion control, soil remediation, building materials and shelter for poultry (CABI, 2014; Devide, 2013; Olabode et al., 2007). It is considered to be a weed in some areas (GISD, 2012). Mexican sunflower is commonly used as fodder for ruminants and rabbits, who can eat the leaves, soft branches and flowers. Its potential has been tested in pigs and poultry (Gualberto et al., 2011; Orwa et al., 2009) with mixed results.

Distribution

Mexican sunflower is native from Mexico and Central America. It was introduced into tropical regions of Asia and Africa, into Australia and several Pacific islands, including Hawaii, French Polynesia and New Caledonia (USDA, 2014). It escaped from cultivation and is now growing wild in many tropical regions (CABI, 2014). In Kenya, Mexican sunflower is one of the most popular indigenous fodder tree species in the sub-humid highlands, where it is frequently coppiced and even uprooted (Roothaert et al., 1997).

Mexican sunflower is a fast-growing plant that tolerates heat and drought and can rapidly form large herbaceous shrubs (CABI, 2014). It is adaptable to most soils. It is found in disturbed areas, abandoned and waste lands, along roadsides and waterways and on cultivated farmlands (GISD, 2012; Olabode et al., 2007). It can be found from sea level up to an altitude of 1500 m (Sosef et al., 1997).

Forage management

Establishment and yields

Mexican sunflower can be easily propagated by direct seeding or by planting of 20-30 cm long cuttings from green stems, at a spacing of 0.5-0.75 m x 0.75 m (Devide, 2013; Orwa et al., 2009). It is easy to grow and does not require fertilizer or special attention (Devide, 2013). It tolerates regular heavy pruning (Sosef et al., 1997). Post-flowering cuttings result in higher yields than pre-flowering cuttings (Devide, 2013). In Côte d’Ivoire, annual biomass yields of 60 t/ha have been obtained at cutting intervals of 4 months (Sosef et al., 1997).

Environmental impact

Weed control and invasiveness

Mexican sunflower is a pioneering species that grows quickly and produces significant amounts of seeds. It can grow from its subterranean stolons and forms dense stands that prevent the growth of young native plants (CABI, 2014). In Thailand, it was used successfully to control Echinochloa colona in rice fields, where it increased rice tillering, leaf area and rice biomass production (Abeysekara et al., 1993). However, Mexican sunflower is considered to be invasive in some parts of Africa and Australia, and in many Pacific islands (CABI, 2014; GISD, 2012).

Crop and soil improver, soil erosion control and soil remediation

Mexican sunflower produces a nutrient-rich (N, K and P) biomass and its positive effect on subsequent rice and maize crops has been reported from Africa and Brazil (Devide, 2013; Olabode et al., 2007; Jama et al., 2000). Its abundance and adaptability, coupled with its rapid growth rate and very high vegetative matter turnover, makes it a candidate species for soil rejuvenation and improvement, as a green manure or as a major component of compost manure. Different practices have been reported: Mexican sunflower can be left to decompose on the field, or it can be turned into green manure (Olabode et al., 2007; Bot et al., 2001). In the latter case, leaves and soft twigs should be cut and chopped into small pieces before flowering and the resulting mixture evenly spread on the ground before being incorporated in the soil (Bot et al., 2001). In Kenya, Mexican sunflower green manure is profitable for high-value crops such as Brassica sp., French beans, tomatoes and Napier grass (Pennisetum purpureum) (Bot et al., 2001). In the Philippines, 1 to 2 tons of freshly chopped Mexican sunflower forage had a positive effect on a sweet potato crop (Pandosen, 1986). From the Philippines, it was also reported that Mexican sunflower could be a potential organic foliar fertilizer for rapeseed (Dela Pena et al., 2013). Mexican sunflower has a positive effect on crop yields when used in intercropping (Orwa et al., 2009).

Mexican sunflower was used to control soil erosion in the Usambara mountains of Tanzania, but it was not as effective as Napier grass or Guatemala grass (Tripsacum andersonii) (Mwango et al., 2014). In Brazil, Mexican sunflower was used for soil remediation along roadsides where heavy metals, and particularly lead, accumulate (Olivares, 2003).

Nutritional aspects

Nutritional attributes

Tithonia diversifolia foliage is rich in protein and comparable to forage legumes in that respect. However, variability is high with protein content ranging from 12% to more than 30% DM, depending on the stage of maturity and on the proportion of stems in the fodder. Likewise, fibre content is highly variable: ADF content varies from 23% to more than 40%. One study found that nutritive value was highest in the vegetative stage and decreased sharply during flowering (Navarro et al., 1990 cited by Perez et al., 2009), but another study reported very low protein values even at the pre-flowering stage (Gualberto et al., 2011). Stems were found to contain less than 10% DM of protein (Pathoummalangsy et al., 2008). Tithonia foliage is rich in minerals (10-16% DM), particularly calcium.

Potential constraints

Antinutritional factors

Mexican sunflower contains limited amounts of secondary metabolites (tannins, flavonoids, esteroids, alkaloids, saponins, terpenoids and anthocyanidins) that can act as antinutritional factors (Delgado et al., 2010). Though these antinutritional factors are in much lower concentrations that in other tropical forages, such as Leucaena leucocephala, it can be useful to reduce their level through air-drying (Odedire et al., 2011; Delgado et al., 2010). Decreases in white blood cell content have been observed in pigs and poultry fed increasing amounts of dried Tithonia diversifolia forage (Olayeni et al., 2006). This could be explained by the presence of terpenoids (sesquiterpene lactones) in the leaves (Dutta et al., 1986).

Ruminants

Mexican sunflower foliage is a valuable fodder for ruminants, due to its high protein content and relatively high digestibility and degradability (Gallego-Castro et al., 2014; Mahecha et al., 2005). However, the expression of this potential requires supplementation with fermentable carbohydrates to improve rumen microbial growth, and/or to increase the supply of bypass protein (Pathoummalangsy et al., 2008). Most studies of Mexican sunflower foliage have involved sheep and goats.

Palatability

In Venezuela, a series of comparisons of the palatability for cattle, sheep and goats of 11 tropical fodders showed that Tithonia diversifolia had a moderate palatability, much lower than that of Chlorophora tinctoria and white mulberry (Morus alba) for all three livestock species. It was less palatable than Leucaena leucocephala but as palatable as Gliricidia sepium for cattle and sheep, though Leucaena and Gliricidia were more palatable to goats. These differences may be explained by the presence of secondary metabolites such as polyphenols, terpens and saponins (Garcia et al., 2008a; Garcia et al., 2008b; Garcia et al., 2008c; Garcia et al., 2009a; Garcia et al., 2009b).

Dairy cattle

Mexican sunflower could be a potentially valuable forage for dairy cows though only one trial had been reported at the time of writing (December 2014). In Colombia, Tithonia diversifolia foliage replaced up to 35% (5.6 kg/d/head of fresh foliage) of the concentrate supplementation for grazing dairy cattle with no effect on milk production and quality (Mahecha et al., 2007).

In Kenya, two experiments assessed the potential of Tithonia diversifolia as a protein supplement for growing goats fed a basal diet of urea-treated maize stover. In the first experiment, Tithonia was found to be a good alternative to Calliandra calothyrsus and Sesbania sesban as a protein supplement, as it resulted in significantly higher daily gain than the other supplements (Wambui et al., 2006b). A second trial showed that Tithonia diversifolia could be included up to a level of 30% (DM basis) in the diet for optimal performance (Wambui et al., 2006b).

In Nigeria, Tithonia diversifolia leaf meal was included at up to 30% (fully replacing soybean meal) in the concentrate, fed to growing goats receiving a basal diet of Guinea grass, with no adverse effect on average daily gain and FCR, though protein digestibility and nitrogen retention were reduced when Tithonia leaf meal was included at more than 10% (Odedire et al., 2014).

Pigs

Mexican sunflower leaf meal

Mexican sunflower leaf meal is rich in protein and, in Nigeria, has been assessed as a potential replacement for soybean meal in pig diets. A first trial found that Mexican sunflower leaf meal could be included in pig diets at up to 20% without significant adverse effects on performance (Olayeni et al., 2006). However, later trials showed that inclusion rates higher than 10% resulted in lower growth performance and N retention, and in poorer FCR (Fasuyi et al., 2013a; Fasuyi et al., 2013b; Fasuyi et al., 2011b). Including mexican sunflower at 10% had no effect on carcass weight but reduced chest width, leg length and back fat (Fasuyi et al., 2012). The inclusion of Mexican sunflower leaf meal negatively affected white blood cells and platelets and, when included at more than 20% in the diet, caused severe epithelial erosion and hemorrages (Fasuyi et al., 2013a; Olayeni et al., 2006).

Mexican sunflower leaf meal is rich in protein but its high fibre content and potential toxicity limit its use in poultry, where it can serve essentially as a substitute for other fibre-rich sources such as cereal bran. Generally, it is not recommended to use Tithonia diversifolia leaf meal in poultry diets, since most feeding trials have reported a reduction in performance when it was included. Only low levels (e.g. 5%) may be used in situations if an economic benefit is required.

In broilers, a decrease in growth was observed at inclusion rates as low as 2.5%, and this effect was amplified at higher levels (Ekeocha, 2012a). Feed intake was also affected above 5% inclusion. Decreased performance and negative effects on reproductive organs were observed in male breeders fed more than 10% Tithonia leaf meal (Togun et al., 2006b). In layers, performance was affected above 10% of the diet, with a significant reduction in feed conversion (Odunsi et al., 1996). In trials with ducks, geese and turkeys, including more than 5-7% Tithonia leaf meal significantly depressed performance, and lower inclusion rates resulted in a level of performance below that obtained with control diets (Ekeocha, 2012c; Ekeocha, 2012d; Ekeocha, 2012e).

Rabbits

Fresh leaves

In several American and African tropical countries, Tithonia diversifolia is commonly used by smallholders as green forage for rabbits; examples are from Bolivia and Venezuela (Nieves et al., 2010; Hernández et al., 2014), Kenya and South-Western Nigeria (Ekeocha, 2012f; Lamidi et al., 2013; Roothaert et al., 1997). Fresh leaves have been used with success as the sole feed for growing rabbits, and in other experiments as the control feed to compare the efficiency of other green forages as sole feeds (Omole et al., 2007). Used as a sole feed, the DM, protein and crude fibre digestibilities of Mexican sunflower foliage are 74, 68 and 63%, respectively, which demonstrates its value as an energy forage and as a source of digestible protein (digestible protein 11% DM). Fresh leaves were also used as a forage distributed with a concentrate in the control diet of studies about the nutritive value of other raw materials (Oluokun, 2005).

Dried leaf meal

Dried leaves of Tithonia diversifolia were used at up to 15-18% in compound diets for growing rabbits, without alteration of growth and slaughter characteristics (Adam, 2013; Nieves et al., 2010; Togun et al., 2006a). The estimated DM and protein digestibility (54% and 64%, respectively, Nieves et al., 2010) were slightly lower than those estimated for the fresh leaves reported above but higher than the average values accepted for dehydrated alfalfa. The calculated digestible energy in this study was 8.94 MJ/kg DM, i.e. about 8% higher than alfalfa (Nieves et al., 2010).

In Nigeria, dried Tithonia leaves were included in the diet of breeding does without alteration of fertility or prolificacy, but the highest tested level was 7.2% of the diet (Ayodele et al., 2014). Several trials in Nigeria have reported good results for growth and reproduction obtained with a 2:1 mixture of Mexican sunflower leaf meal and dried blood, mostly replacing oil meals. The inclusion of this mixture at up to 15% of the diet induced similar or slightly improved growth performance without alteration of serum parameters or reproductive aptitudes of males (Ajayi et al., 2007; Ajayi et al., 2009; Ajayi et al., 2012; Olabanji et al., 2007a; Olabanji et al., 2007b). The addition of dried blood to Mexican sunflower leaf meal enhanced the already high concentration of lysine in the leaf protein but worsened the deficit in sulphur-containing amino acids. Generally, it is recommended to include other sources of sulphur-containing amino acids, such as cereals or cereal by-products, to obtain a balanced ration based on Tithonia leaves, particularly if blood meal is included in the diet.

Veterinary medicine

For rabbits suffering from scabies, a recurring skin problem of rabbits raised in tropical countries, a Tithonia leaf extract (300 g of leaves extracted in 100 ml of water) applied 4 times per day over a period of 5 days on the affected areas was as efficient as ivermectin to treat the condition (Vu Thi Thu Hang et al., 2012).